When a oxygen sensor comprising a sensor device is exposed as an air/fuel ratio sensor to an exhaust gas upon using lead-containing fuels, electrodes are contaminated with lead, phosphorus, silicon or the like and degraded with lapse of time to no more provide sufficient electromotive force. Sensors coping with the problem of deterioration for the durability of electrodes are disclosed, for example, in Japanese Patent Publication No. 90176/1994 and Japanese Laid-Open No. 113480/1997. However, a sensor capable of completely preventing contamination to electrodes in a low temperature region which is most likely to undergo the effect of lead or the like contained in exhaust gases has not yet been obtained.
This invention intends to provide an oxygen sensor having a sensor device capable of preventing an electrode from contamination by lead or the like and having excellent durability even in contact with exhaust gases at a relatively low temperature, as well as a method of manufacturing such a sensor device.